#include <stdio.h>
#define NR 50005
/*
int scrie(int p,int u,int d[],int v[])
{
	int i;
	for (i=p; i<=u; i++)
		printf("%d ",v[d[i]]);
	printf("\n");
}
*/
int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	int n,k,i,v[NR],p,u,d[NR],s=0;
	scanf("%d%d",&n,&k);
	for (i=1; i<=n; i++)
		scanf("%d",&v[i]);
	p=1;u=0;
	d[++u]=1;
	for (i=2; i<=k; ++i)
	{
		while (u>=p && v[d[u]]>=v[i])
			--u;
		d[++u]=i;
		//scrie(p,u,d,v);
	}
	s=v[d[p]];
	//printf("%d\n",v[d[p]]); 
	for (i=k+1; i<=n; ++i)
	{
		while (d[p]<i-k+1)
			++p;
		while(u>=p && v[d[u]]>=v[i])
			--u;
		d[++u]=i;
		s+=v[d[p]];
		//scrie(p,u,d,v);
		//printf("%d\n",v[d[p]]); 
	}
	printf("%d\n",s);
	return 0;
}